1. Field of the Invention
This invention relates to a semiconductor light-emitting device. This semiconductor light-emitting device can be utilized as a light-emitting diode, a laser diode, or the like.
2. Description of the Conventional Art
Light-emitting devices using compound semiconductors cover visible short wavelength regions. Among other light-emitting diodes, nitride III semiconductors have attracted attention in recent years because these semiconductors are direct transition semiconductors, so that they exhibit high light-emitting efficiency, and because these semiconductors emit blue light, which is one of the three primary colors.
When the light-emitting layer is formed of InXGa1−XN, it has heretofore been considered that a relation such as shown by the dashed line in FIG. 1 exists between the indium mole fraction X and the photon energy (see “Journal of applied physics”, Vol. 46, No. 8, August 1975, pp. 3432-3437 and “Microelectronics Journal”, 25 (1994), pp. 651-659). The photon energy of the wavelength λ of blue light (470 nm) is almost 2.64 eV, and the photon energy of the wavelength λ of green light (520 nm) is almost 2.38 eV. Therefore, according to the conventionally proposed relation, blue emission is obtained by setting the indium mole fraction X to approximately 0.26 and green emission is obtained by setting the indium mole fraction X to approximately 0.67 if no impurities are to be added.
As a result of a continued study on the light-emitting layer formed of InXGa1−XN, the inventors realized that the conventionally proposed relationship shown by the dashed line in FIG. 1 could not be applied without modification if such a light-emitting layer is to be formed on a sapphire substrate.